Liquid lens structure with adjustable optical power

ABSTRACT

A liquid lens structure has an adjustable and continuous range of optical power. The liquid lens structure comprises a substrate layer and a deformable membrane which enclose a volume of liquid. The substrate layer is at least partially transparent in the optical band. The deformable membrane comprises a ground layer, two membrane layers, and two conductive layers. Each of the two conductive layers control electrical voltage applied to one of the membrane layers in reference to the ground layer, wherein each membrane layer deforms in response to applied electrical voltage. The deformation of the two membrane layers adjusts a curvature of the deformable membrane which provides the adjustable continuous range of optical power to the liquid lens structure.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. Application No.15/870,443, filed Jan. 12, 2018, which is incorporated by reference inits entirety.

BACKGROUND

The present disclosure generally relates to varifocal lens structures,more specifically to a liquid lens structure with an adjustable opticalpower.

Artificial reality systems conventionally utilize a head-mounted display(HMD) to simulate virtual or augmented environments. For example,stereoscopic images can be displayed on an electronic display inside theHMD to simulate the illusion of depth and position sensors can be usedto estimate what portion of the virtual environment is being viewed bythe user. Such a simulation, however, can cause visual fatigue andnausea resulting from an inability of conventional optical systems ofHMDs to correctly render or otherwise compensate for vergence andaccommodation conflicts.

SUMMARY

A varifocal block has a continuous range of adjustment of optical power.The varifocal block includes at least a liquid lens structure with acontinuous range of adjustment of optical power. The liquid lensstructure comprises a substrate layer and a deformable membrane whichenclose a volume of liquid. The substrate layer is at least partiallytransparent in the optical band. The deformable membrane comprises aground layer, two piezoelectric membrane layers, and two conductivelayers. Each of the two conductive layers control electrical voltageapplied to one of the piezoelectric membrane layers, wherein eachpiezoelectric membrane layer deforms in response to applied electricalvoltage. The deformation of the two piezoelectric membrane layersadjusts a curvature to the deformable membrane which provides thecontinuous range of optical power to the liquid lens structure.

The varifocal block may be part of a head-mounted display (HMD) withinan artificial reality system. The HMD presents content via an electronicdisplay to a wearing user at a focal distance. The varifocal blockpresents the content over a plurality of image planes that areassociated with different optical powers of the varifocal block. Asnoted above, the varifocal block has a continuous range of adjustment ofoptical power. Each value of optical power over the continuous range ofadjustment of optical power corresponds to a different image plane ofthe plurality of image planes. In some embodiments, the varifocal blockadjusts the image plane location in accordance with instructions fromthe HMD to, e.g., mitigate vergence accommodation conflict of eyes ofthe wearing user. The image plane location is adjusted by adjusting anoptical power associated with the varifocal block, and specifically byadjusting the optical powers associated with the liquid lens structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is cross sectional view of a liquid lens structure at a firstoptical power, in accordance with an embodiment.

FIG. 1B is cross sectional view of the liquid lens structure of FIG. 1Aat a second optical power, in accordance with an embodiment.

FIG. 2A is a top plan view of a conductive layer with non-intersectingconductive wires, in accordance with one or more embodiments.

FIG. 2B is a top plan view of a conductive layer with intersectingconductive wires, in accordance with one or more embodiments.

FIG. 2C is a top plan view of a conductive layer with addressable nodes,in accordance with one or more embodiments.

FIG. 2D is a top plan view of a portion of a conductive layer withconductive branching, in accordance with one or more embodiments.

FIG. 3A is a perspective view of a head-mounted display (HMD), inaccordance with one or more embodiments.

FIG. 3B is a cross sectional view of the front rigid body of the HMD ofFIG. 3A, in accordance with one or more embodiments.

FIG. 4 is a block diagram of an artificial reality system in which theHMD of FIG. 3 operates, in accordance with one or more embodiments.

DETAILED DESCRIPTION Configuration Overview

An artificial reality system includes a head-mounted display (HMD). TheHMD includes at least a varifocal block. The HMD of an artificialreality system presents content via an electronic display to a wearinguser at a focal distance. The varifocal block adjusts the focal distancein accordance with instructions from the HMD to, e.g., mitigate vergenceaccommodation conflict of eyes of the wearing user. The focal distanceis adjusted by adjusting an optical power associated with the varifocalblock, and specifically by adjusting the optical powers associated withone or more varifocal structures within the varifocal block. Thevarifocal block can have one or more varifocal structures and otheroptical devices in optical series. Optical series refers to relativepositioning of a plurality of optical devices such that light, for eachoptical device of the plurality of optical devices, is transmitted bythat optical device before being transmitted by another optical deviceof the plurality of optical devices. Moreover, ordering of the opticaldevices does not matter. For example, optical device A placed beforeoptical device B, or optical device B placed before optical device A,are both in optical series. Similar to electric circuitry design,optical series represent optical devices with their optical propertiescompounded when placed in series.

A varifocal structure is an optical device that is configured todynamically adjust its focus in accordance with instructions from theartificial reality system. The varifocal structure is a liquid lensstructure in this present disclosure. The liquid lens structuresincludes at least a substrate layer and a deformable membrane with avolume of liquid enclosed between the substrate layer and the deformablemembrane. The deformable membrane comprises at least a ground layer witha plurality of conductive layers coupled to a plurality of membranelayers such that the curvature of the plurality of membrane layersdepend on voltages applied by the plurality of conductive layers.

The liquid lens structure is an optical device that is able to adjustfocus (i.e., optical power) over a continuous range from a positivevalue to a negative value. There are fixed volume fluid filled lenses,and variable volume fluid-filled lenses. For HMD applications, afixed-volume liquid lens can be preferable for many reasons. Forexample, the fixed-volume liquid lens offers a compact design, a largeclear aperture size and a stable optical performance within the variablefocus range (e.g. no air bubble, freedom on the frame/lens shape). Inthis application, a liquid lens structure with a deformable membrane hasa continuous range of 0 to F (in terms of optical power this may berepresented as 0 to D.

The HMD of an artificial reality system presents artificial realitycontent to a wearing user. Artificial reality content may includecompletely generated content or generated content combined with captured(e.g., real-world) content. The artificial reality content may includevideo, audio, haptic sensation, or some combination thereof, and any ofwhich may be presented in a single channel or in multiple channels (suchas stereo video that produces a three-dimensional effect to the viewer).Additionally, in some embodiments, artificial reality may also beassociated with applications, products, accessories, services, or somecombination thereof, that are used to, e.g., create content in anartificial reality and/or are otherwise used in (e.g., performactivities in) an artificial reality. The artificial reality system thatprovides the artificial reality content may be implemented on variousplatforms, including a head-mounted display (HMD) connected to a hostcomputer system, a standalone HMD, a mobile device or computing system,or any other hardware platform capable of providing artificial realitycontent to one or more viewers.

Vergence-Accommodation Overview

Vergence-accommodation conflict is a problem in many artificial realitysystems. Vergence is the simultaneous movement or rotation of both eyesin opposite directions to obtain or maintain single binocular vision andis connected to accommodation of the eye. Under normal conditions, whenhuman eyes look at a new object at a distance different from an objectthey had been looking at, the eyes automatically change focus (bychanging their shape) to provide accommodation at the new distance orvergence depth of the new object. In an example, a user is looking at areal object. As the real object is moved closer or farther to the user,each eye rotates inward or outward (i.e., convergence or divergence) tostay verged on the real object. As the real object moves, the eyes must“accommodate” for the different focal distance of the real object bychanging its shape to reduce the power or focal length. In artificialreality, virtual objects need to be presented.

In artificial reality systems, a virtual object is presented on theelectronic display of the HMD that is part of the artificial realitysystem. The light emitted by the HMD is configured to have a particularfocal distance, such that the virtual scene appears to a user at aparticular focal plane. As the content to be rendered movescloser/farther from the user, the HMD correspondingly instructs thevarifocal block to adjust the focal distance to mitigate a possibilityof a user experiencing a conflict with eye vergence and eyeaccommodation. Additionally, in some embodiments, the HMD may track auser’s eyes such that the artificial reality system is able toapproximate gaze lines and determine a gaze point including a vergencedepth (an estimated point of intersection of the gaze lines) todetermine an appropriate amount of accommodation to provide the user.The gaze point identifies an object or plane of focus for a particularframe of the virtual scene and the HMD adjusts the distance of thevarifocal block to keep the user’s eyes in a zone of comfort as vergenceand accommodation change.

Varifocal Liquid Lens Structure

FIG. 1A is cross sectional view of a liquid lens structure 100 at afirst optical power, in accordance with an embodiment. The liquid lensstructure 100 comprises a deformable membrane 110, a substrate layer150, a liquid layer 160, and a plurality of electrodes 170. Inaccordance with one or more embodiments, the liquid lens structure 100has the liquid layer 160 coupled between the deformable membrane 110 andthe substrate layer 150. The plurality of electrodes 170 are along aperipheral edge of the liquid lens structure 100. The deformablemembrane 110 comprises a ground layer 115, a first adjustable membrane120, a first conductive layer 125, a second adjustable membrane 130, anda second conductive layer 135. The liquid lens structure 100 is anoptical device that is able to adjust focus (i.e., optical power) over acontinuous range by adjusting a tunable curvature to the deformablemembrane 110.

The deformable membrane 110 changes its curvature to provide anadjustable focus of the liquid lens structure 100. An edge of thedeformable membrane 110 is fixed along the peripheral edge of the liquidlens structure 100 such that the deformable membrane is electricallycoupled to the plurality of electrodes 170. The deformable membrane 110may be fixed along the peripheral edge with some amount of tension or notension applied to the deformable membrane 110. Additionally, tensioncan be applied to the deformable membrane 110 after its edge is fixedalong the peripheral edge of the liquid lens structure 100. Thedeformable membrane 110 comprises the ground layer 115, the firstadjustable membrane 120, the first conductive layer 125, the secondadjustable membrane 130, and the second conductive layer 135. The sideof the deformable membrane 110 that is in contact with the liquid layer160 is defined as an interior side; whereas a side opposite that of theinterior side is defined as an exterior side. In accordance with anembodiment, the ground layer 115 is coupled between the first adjustablemembrane 120 and the second adjustable membrane 130. The firstconductive layer 125 is coupled to the first adjustable membrane 120 onthe exterior side of the deformable membrane 110. The second conductivelayer 135 is coupled to the second adjustable membrane 130 on theinterior side of the deformable membrane 110. Through adjusting a firstvoltage through the first adjustable membrane 120 and a second voltagethrough the second adjustable membrane 130, the deformable membrane cancontrol mechanical strain of the first adjustable membrane 120 and thesecond adjustable membrane 130. The controllable mechanical strain ofthe first adjustable membrane 120 and of the second adjustable membrane130 provides a continuous range of curvature of the deformable membrane110. In accordance with the illustration of FIG. 1A, the deformablemembrane 110 has no induced curvature thus setting the liquid lensstructure 100 at a first optical power either additive or subtractive.Although the deformable membrane 110 has no induced curvature, othercomponents of the liquid lens structure 100 can add or subtract opticalpower to the liquid lens structure 100.

The ground layer 115 of the deformable membrane 110 is configured as areference for voltage differences applied to the first conductive layer125 and the second conductive layer 135. The ground layer 115 iscomposed of a flexible and thin conductive material. The ground layer115 is substantially transparent such that the ground layer 115transmits some amount of light. For example, the flexible and thinconductive material can be a conductive metal that is substantiallytransparent, e.g., Indium Tin Oxide (ITO), Aluminum Zinc Oxide (AZO),etc., in accordance with one or more embodiments. The ground layer 115is coupled to one or more electrodes of the plurality of electrodes 170.In accordance with some embodiments, the ground layer 115 is aconductive wire mesh.

The first adjustable membrane 120 undergoes mechanical strain inresponse to an applied voltage. The first adjustable membrane 120 iscomposed of substantially transparent piezoelectric material thatstrains in at least one dimension when an electrical voltage is applied.For example, the first adjustable membrane 120 is composed ofpolyvinylidene difluoride (PVDF) which is a polymer piezoelectricmaterial. In other examples, other piezoelectric materials can be usedto construct the first adjustable membrane 120. Additionally, otherelectroactive polymers, elastomers, and gels may be used. For examplepoled or un-poled PVDF, poled or unpoled PVDF:TfPE copolymers and othercopolymers of PVDF, acrylics including, for example, 3M™ VHB™ adhesive,and silicones including polydimethylsilicone (PDMS). The polymer may beused as a bimorph, where there are two bonded electroactive materials,or a unimorph, where an electroactive material is bonded to anon-activated material. The non-activated material may inherently have alow mechanical response to electric fields (for example glass,polyethylene terephthalate, polycarbonate, cyclic polyolefins, etc.), ormay be an electroactive material that does not experience substantiallychanging electric fields. As an electrical voltage is applied to thefirst adjustable membrane 120, the first adjustable membrane 120 strainsin at least one dimension. As the first adjustable membrane 120 is acomponent of the deformable membrane 110, likewise an edge of the firstadjustable membrane 120 is fixed along the peripheral edge of the liquidlens structure 100. In some embodiments, the edge of the firstadjustable membrane 120 is fixed along the peripheral edge of the liquidlens structure 100 while the first adjustable membrane 120 maintainssome tension. In other embodiments, there is no tension initiallypresent when the edge of the first adjustable membrane 120 is fixed.Additionally in some embodiments, some tension is applied to the firstadjustable membrane 120 after its edge is fixed. As the first adjustablemembrane 120 strains, a first curvature is induced within the firstadjustable membrane 120.

The first conductive layer 125 conducts electricity to provide a voltagedifference through the first adjustable membrane 120. The firstconductive layer 125 is composed of a flexible and thin conductivematerial. Similarly in the material composition of the ground layer 115,the first conductive layer 125 can be a conductive metal which issubstantially transparent, in accordance with one or more embodiments.For example, the first conductive layer 125 can be composed of ITO, acopper metal mesh, metallic nanowires, metal oxide nanowires, etc. Inother embodiments, the ground layer 115 is a conductive film. In otherembodiments, the thin conductive layer can be made from filaments suchas carbon nanotubes or metal (e.g. silver or gold) nanowires dispersedin a matrix such as a polymer binder. In other embodiments, thetransparent conductive coating can be a conductive polymer such aspoly(3,4-ethylenedioxythiophene) (PEDOT),poly(3,4-ethylenedioxythiophene) (PEDOT):poly(styrene sulfonate) (PSS),or poly(4,4-dioctyl cyclopentadithiophene). These conductive polymersmay also be doped. The transparent conductive coating may also becombinations of these different conductive materials.

The first conductive layer 125 is also coupled to one or more electrodesof the plurality of electrodes 170. In reference to the ground layer115, the first conductive layer 125 adjusts the first voltage throughthe first adjustable membrane 120. In one or more embodiments, the firstconductive layer 125 comprises a plurality of conductive wires. In someembodiments, the plurality of conductive wires are non-intersecting;whereas, in other embodiments, the plurality of conductive wires areintersecting. For example, embodiments wherein the plurality ofconductive wires are non-intersecting, the plurality of conductive wiresare arranged in a parallel fashion. In some embodiments, the firstconductive layer 125 contains at least two or more differing voltages totwo or more points of the first conductive layer 125 through the firstadjustable membrane 120. The two or more differing voltages provides twoor more differing curvatures to portions of the first adjustablemembrane 120. In other embodiments, the first conductive layer 125comprises a plurality of conductive wires which are placed in ameandering pattern, e.g., zig zag, serpentine, sinusoidal, etc., so asto reduce noticeability by a user.

The second adjustable membrane 130 and the second conductive layer 135are similar to the first adjustable membrane 120 and the firstconductive layer 125, thus the detailed description thereof is omittedherein for the sake of brevity. In some embodiments, the firstadjustable membrane 120 and the second adjustable membrane 130 may haveuniform dimensions (e.g. uniform thickness, uniform surface area, etc.)and/or may be constructed from uniform materials with uniformproperties. In other embodiments, the first adjustable membrane 120 andthe second adjustable membrane 130 may have differing dimension and/ormay be constructed from differing materials with different properties.In these embodiments, the differences between the first adjustablemembrane 120 and the second adjustable membrane 130 can be used to formvarious lens shapes (e.g. aspherical, cylindrical, etc.). In moreembodiments, one or both of the first adjustable membrane 120 and thesecond adjustable membrane 130 maintain some amount of tension.Similarly, there are embodiments where the first conductive layer 125and the second conductive layer 135 are uniform in shape, material,properties, pattern, etc. with other embodiments where the two differ inone or more factors.

The substrate layer 150, the plurality of electrodes 170, and thedeformable membrane 110 enclose the liquid layer 160. The substratelayer 150 is substantially transparent in the visible band (-380 nm to~750 nm). In some embodiments, the substrate layer 150 is alsotransparent in some or all of the infrared band (~750 nm to 1000 nm).The substrate layer 150 may be composed of e.g., SiO₂, plastic,sapphire, thermoplastics, etc. In some embodiments, the substrate layer150 is flat such that the substrate layer 150 does not contribute to theoptical power of the liquid lens structure 100. In other embodiments,the substrate layer 150 is curved contributing to the optical power ofthe liquid lens structure 100. For example, the substrate layer 150 maybe formed to act as an aspherical lens, a spherical lens, a freeformoptic, a Fresnel lens, or have some other optical element that providesa fixed amount of optical power. The substrate layer 150 may also act asa foundation for additional components or additional optical devices tothe liquid lens structure 100. For example, coupled to the substratelayer 150 is an optical filter, a waveplate, a polarizer, a lens,another optical device, or a combination thereof.

The liquid layer 160 is a volume of liquid of the liquid lens structure100. The liquid layer 160 includes one or more liquids which aresubstantially transparent in an optical band of interest. The volume ofliquid in the liquid layer 160 is constant or variable. In theillustration of FIG. 1B, the liquid layer 160 of the liquid lensstructure 100 is variable such that in FIG. 1B, there is a greatervolume of fluid in the liquid layer 160 compared to that in FIG. 1A. Theone or more liquids which comprise the liquid layer 160 have refractiveindices between 1.2 and 2.5. Suitable fluids include fluorocarbons,silicone oils, including fluid available from Dow Chemical, phenylsilicones, high index fluids containing bromine, iodine, or sulfur, orcombinations thereof. The refractive indices of the one or more liquidsinfluences the range of continuous optical power for the liquid lensstructure 100. For example, given a certain range for curvature of thedeformable membrane, a liquid layer 160 with a higher refractive indexwould result in a liquid lens structure 100 with a larger range ofcontinuous optical power in comparison to a liquid layer 160 with alower refractive index.

The plurality of electrodes 170 provides an electrical voltage to thedeformable membrane 110 from a variable voltage supply. The plurality ofelectrodes 170 is coupled to the variable voltage supply (not shown inFIGS. 1A nor 1B) and to the ground layer 115, the first conductive layer125, and the second conductive layer 135 of the deformable membrane 110.Of the plurality of electrodes 170, there are at least three subsets ofelectrodes. A first subset of electrodes is coupled to the ground layer115; a second subset of electrodes is coupled to the first conductivelayer 125; a third subset of electrodes is coupled to the secondconductive layer 135. The plurality of electrodes 170 provides variableelectrical voltages such that liquid lens structure 100 has the tunablecurvature of the deformable membrane 110. In some embodiments, eachsubset of electrodes provides two or more differing voltages to two ormore portions of the deformable membrane 110; thus the deformablemembrane 110 can have one or more portions with differing curvatures.For example, a first voltage of a first polarity and first magnitude isapplied to the first conductive layer 125; whereas a second voltage of asecond polarity and a second magnitude is applied to the secondconductive layer 135. In another example, a first voltage of a firstpolarity and a first magnitude is applied to a portion of the firstconductive layer 125; whereas, a second voltage of a second polarity anda second magnitude is applied to another portion of the first conductivelayer 125. In these embodiments, portions of the deformable membrane 110with differing curvatures add or subtract varying degrees of opticalpower to the liquid lens structure 100.

FIG. 1B is cross sectional view of the liquid lens structure 100 of FIG.1A at a second optical power, in accordance with an embodiment. Inaccordance with this illustration, the deformable membrane 110 is curvedspherically such that the deformable membrane 110 provides the secondoptical power. The first voltage applied through the first adjustablemembrane 120 along with the second voltage applied through the secondadjustable membrane 130 curves the deformable membrane 110 to providethe spherical curvature. From the spherical curvature, the liquid lensstructure 100 has the second optical power which is larger in magnitudethan the first optical power as shown in FIG. 1A. With the deformablemembrane 110 able to change its curvature in a continuous fashion, theliquid lens structure 100 has a continuous range of optical power. Thiscontinuous range of optical power can range anywhere from -2 Diopters to+2 Diopters.

The continuous range of optical power that the liquid lens structure 100has provides an adjustable range of focal distance. In accordance withone or embodiments, the liquid lens structure 100 can be an opticaldevice of a varifocal block in a HMD. A focal distance of the varifocalblock depends in part on the continuous range of optical power of theliquid lens structure 100. The liquid lens structure 100, in theseembodiments, can be controlled to aid in adjusting the focal distance ofthe varifocal block in accordance with instructions from the HMD to,e.g., mitigate vergence accommodation conflict of eyes of the wearinguser.

Conductive Layer Configurations

FIG. 2A is a top plan view of a conductive layer 200 withnon-intersecting conductive wires 210, in accordance with one or moreembodiments. The conductive layer 200 can be at least one of the groundlayer 115, the first conductive layer 125, and the second conductivelayer 135 of the liquid lens structure 100 of FIG. 1 . In someembodiments (as shown by the illustration), the non-intersectingconductive wires 210 are coplanar and spaced evenly in a parallelfashion. The non-intersecting conductive wires 210 can also be arrangedin a skew fashion such that the non-intersecting conductive wires areskew (not shown in this illustration). In some embodiments, all thenon-intersecting conductive wires 210 are coupled to one electrode suchas one electrode of the plurality of electrodes 170 of the liquid lensstructure 100 of FIG. 1 . In other embodiments, a first conductive wireof the non-intersecting conductive wires 210 is coupled to a firstelectrode with a second conductive wire of the non-intersectingconductive wires 210 coupled to a second electrode such that the firstconductive wire completes a different circuit from the second conductivewire. In these embodiments, the conductive layer 200 can provide aplurality of voltages to different conductive wires of thenon-intersecting conductive wires 210. In the context of the liquid lensstructure 100, the conductive layer 200 (as one of the ground layer 115,the first conductive layer 125, and the second conductive layer 135) canprovide a plurality of voltages to different portions of a correspondingadjustable membrane to introduce at least two curvatures to thecorresponding adjustable membrane. In accordance with some embodimentswith the non-intersecting conductive wires 210 spaced evenly in aparallel fashion, the conductive layer 200 can curve a correspondingadjustable membrane in one dimension. In other variations, thenon-intersecting conductive wires 210 can vary in spacing with thenumber of non-intersecting conductive wires 210 also varying.

FIG. 2B is a top plan view of a conductive layer 220 with intersectingconductive wires 230, in accordance with one or more embodiments. Theconductive layer 220 can be at least one of the ground layer 115, thefirst conductive layer 125, and the second conductive layer 135 of theliquid lens structure 100 of FIG. 1 . In some embodiments (as shown bythe illustration), the intersecting conductive wires 230 are coplanarand arranged in a crosshatch pattern. In this illustration, theintersecting conductive wires 230 are in a crosshatch pattern,specifically a square grid. In some embodiments, all the intersectingconductive wires 230 are coupled to one electrode such as one electrodeof the plurality of electrodes 170 of the liquid lens structure 100 ofFIG. 1 . In these embodiments, the conductive layer 200 provides onevoltage over all the intersecting conductive wires 230. In the contextof the liquid lens structure 100, the conductive layer 220 (as one ofthe ground layer 115, the first conductive layer 125, and the secondconductive layer 135) provides one voltage over an entirety of acorresponding adjustable membrane to introduce one curvature to thecorresponding adjustable membrane.

FIG. 2C is a top plan view of a conductive layer 240 with addressablenodes, in accordance with one or more embodiments. The conductive layer240 can be at least one of the ground layer 115, the first conductivelayer 125, and the second conductive layer 135 of the liquid lensstructure 100 of FIG. 1 . The conductive layer 240 comprises conductivewires 250 (such as those described in FIG. 2A or FIG. 2B) with theability to provide a plurality of addressable nodes with varyingvoltages. In accordance with this illustration, there is a first node255 and a second node 260 of the plurality of addressable nodes. Theconductive layer 240 can provide a first voltage to the first node 255and a second voltage to the second node 260 in tandem such that acorresponding first portion of an adjustable membrane can differ in itsinduced curvature from that of a corresponding second portion of theadjustable membrane. For example, a first half of the conductive layer240 can induce a first optical power in the liquid lens structure 100with a second half of the conductive layer 240 inducing a second opticalpower in the liquid lens structure 100. This functionality can provide abifocal feature to the liquid lens structure 100. This functionality canalso be used to correct for optical aberrations or distortions, e.g.,astigmatism, field curvature, etc.

FIG. 2D is a top plan view of a portion of a conductive layer withconductive branching 280, in accordance with one or more embodiments.The embodiments described herein can be implemented in any embodimentsof the conductive layers as described in FIGS. 2A - 2C. The conductivebranching 280 can be incorporated into a conductive layer, wherein theconductive layer is at least one of the ground layer 115, the firstconductive layer 125, and the second conductive layer 135 of the liquidlens structure 100 of FIG. 1 . The conductive branching 280 builds aplurality of conductive branches 290 off of a portion of a conductivewire 285 (such as those described in FIG. 2A or FIG. 2B). The conductivebranches 290 branch off the conductive wire 285 in a variety ofpatterns. In the illustrative example of FIG. 2D, there is a subset ofconductive branches of the plurality of conductive branches 290 whichintersect the conductive wire 280 and other conductive branches of theplurality of conductive branches 290 which intersect the subset. Inother embodiments, the plurality of conductive branches 290 onlyintersect the conductive wire 285. The plurality of conductive branches290 help to spread a voltage applied through the conductive wire 285over a bigger area. In the context of the liquid lens structure 100, theconductive layer with the conductive branching 280 (as one of the groundlayer 115, the first conductive layer 125, and the second conductivelayer 135) provides a voltage over a wider area of a correspondingadjustable membrane to introduce a more uniform curvature to thecorresponding adjustable membrane.

In accordance with other embodiments, a conductive layer can haveconductive branching in a meandering pattern. In the illustration ofFIG. 1 , the conductive branching 280 configures the conductive layerwith straight wires, branching off one another in an orthogonal pattern.In various other embodiments, the conductive branching has themeandering pattern with a similar purpose of spreading voltage appliedthrough the conductive layer over a larger area. The meandering patternscan vary such as zigzag, serpentine, sinusoidal, other curves. Theconductive branching can build off of these meandering patterns withbranches intersecting the meandering conductive wires. In additionalembodiments, a subset of the conductive wires of the conductive layercan meander in accordance with one pattern with another subset of theconductive wires meandering in accordance with another pattern. Themeandering pattern of the conductive branching reduces noticeability ofthe conductive layer to a user as there is less ordering to theconductive branching.

Head-Mounted Display Configuration Overview

FIG. 3A is a perspective view of a head-mounted display 300 (HMD 300),in accordance with one or more embodiments. The HMD 300 presents contentto a user. The HMD 300 includes a front rigid body 305 and a band 310.The band 310 secures the front rigid body 305 to a user’s head. Thefront rigid body 305 includes one or more electronic display elements ofan electronic display (shown in FIG. 3B), an IMU 315, the one or moreposition sensors 320, and the locators 325. In the embodiment shown byFIG. 3A, the position sensors 320 are located within the IMU 315, andneither the IMU 315 nor the position sensors 320 are visible to theuser. The IMU 315, the position sensors 320, and the locators 325 arediscussed in detail below with regard to FIG. 4 . Note in embodimentswhere the HMD 300 acts as an AR or MR device, portions of the HMD 300and its internal components are at least partially transparent.

FIG. 3B is a cross sectional view 350 of the front rigid body 305 of theHMD 300 of FIG. 3 , in accordance with one or more embodiments. As shownin FIG. 3B, the front rigid body 305 includes an electronic displayelement 355 and a varifocal block 360 that together are incorporated soas to provide image light to an eye 365 of a user. The eye 365 of a useris typically positioned at the front rigid body 305. For purposes ofillustration, FIG. 3B shows a cross sectional view 350 associated withthe single eye 365, but another varifocal block 360, separate from thevarifocal block 360 shown in this illustration, provides altered imagelight to another eye 365 of the user.

The electronic display element 355 displays images to the user. Invarious embodiments, the electronic display element 355 may comprise asingle electronic display or multiple electronic displays (e.g., adisplay for each eye of a user). Examples of the electronic displayelement 355 include: a liquid crystal display (LCD), an organic lightemitting diode (OLED) display, an active-matrix organic light-emittingdiode display (AMOLED), a QOLED, a QLED, a microLED, some other display,or some combination thereof.

The varifocal block 360 adjusts an orientation from light emitted fromthe electronic display element 355 such that it appears at particularfocal distances from the user. The varifocal block 360 includes one ormore optical devices in optical series. An optical device may beconfigured to dynamically adjust its focus in accordance withinstructions from an artificial reality system. The varifocal block 360may include the liquid lens structure 100 as described in FIG. 1 toadjust its focus.

Artificial Reality System Overview

FIG. 4 is a block diagram of an artificial reality system 400 in whichthe HMD 405 operates, in accordance with one or more embodiments. Theartificial reality system 400 may be for use as a virtual reality (VR)system, an augmented reality (AR) system, a mixed reality (MR) system,or some combination thereof. In this example, the artificial realitysystem 400 includes the HMD 405, an imaging device 410, and an inputinterface 415, which are each coupled to a console 420. While FIG. 4shows a single HMD 405, a single imaging device 410, and a single inputinterface 415, in other embodiments, any number of these components maybe included in the artificial reality system 400. For example, there maybe multiple HMDs 300 each having an associated input interface 415 andbeing monitored by one or more imaging devices 410, with each HMD 405,input interface 415, and imaging devices 410 communicating with theconsole 420. In alternative configurations, different and/or additionalcomponents may also be included in the artificial reality system 400.

The HMD 405 may act as an artificial reality HMD. An MR and/or AR HMDaugments views of a physical, real-world environment withcomputer-generated elements (e.g., images, video, sound, etc.). The HMD405 presents content to a user. In some embodiments, the HMD 405 is anembodiment of the HMD 405. Example content includes images, video,audio, or some combination thereof. Audio content may be presented via aseparate device (e.g., speakers and/or headphones) external to the HMD405 that receives audio information from the HMD 405, the console 420,or both. The HMD 405 includes locators 425, inertial measurement units(IMU) 430, position sensors 435, an electronic display 440, and avarifocal block 445 (similar the varifocal block 360 described in FIG.3B). Additionally the HMD 405 may include an eye tracking module 450, avergence processing module 455, and a scene rendering module 460.

The locators 425 are objects located in specific positions on the HMD405 relative to one another and relative to a specific reference pointon the HMD 405. The locators 325 are an embodiment of the locators 425.A locator 425 may be a light emitting diode (LED), a corner cubereflector, a reflective marker, a type of light source that contrastswith an environment in which the HMD 405 operates, or some combinationthereof. Active locators 425 (i.e., an LED or other type of lightemitting device) may emit light in the visible band (~380 nm to 750 nm),in the infrared (IR) band (~440 nm to 1700 nm), in the ultraviolet band(10 nm to 380 nm), some other portion of the electromagnetic spectrum,or some combination thereof.

The locators 425 can be located beneath an outer surface of the HMD 405,which is transparent to the wavelengths of light emitted or reflected bythe locators 425 or is thin enough not to substantially attenuate thewavelengths of light emitted or reflected by the locators 425. Further,the outer surface or other portions of the HMD 405 can be opaque in thevisible band of wavelengths of light. Thus, the locators 425 may emitlight in the IR band while under an outer surface of the HMD 405 that istransparent in the IR band but opaque in the visible band.

As described above with reference to FIGS. 3A-B, the IMU 430 is anelectronic device that generates IMU data based on measurement signalsreceived from one or more of the position sensors 435, which generateone or more measurement signals in response to motion of HMD 405.Examples of the position sensors 435 include accelerometers, gyroscopes,magnetometers, other sensors suitable for detecting motion, correctingerror associated with the IMU 430, or some combination thereof.

Based on the measurement signals from the position sensors 435, the IMU430 generates IMU data indicating an estimated position of the HMD 405relative to an initial position of the HMD 405. For example, theposition sensors 435 include multiple accelerometers to measuretranslational motion (forward/back, up/down, left/right) and multiplegyroscopes to measure rotational motion (e.g., pitch, yaw, and roll).The IMU 430 can, for example, rapidly sample the measurement signals andcalculate the estimated position of the HMD 405 from the sampled data.For example, the IMU 430 integrates measurement signals received fromthe accelerometers over time to estimate a velocity vector andintegrates the velocity vector over time to determine an estimatedposition of a reference point on the HMD 405. The reference point is apoint that may be used to describe the position of the HMD 405. Whilethe reference point may generally be defined as a point in space, invarious embodiments, a reference point is defined as a point within theHMD 405 (e.g., a center of the IMU 130). Alternatively, the IMU 430provides the sampled measurement signals to the console 420, whichdetermines the IMU data.

The IMU 430 can additionally receive one or more calibration parametersfrom the console 420. As further discussed below, the one or morecalibration parameters are used to maintain tracking of the HMD 405.Based on a received calibration parameter, the IMU 430 may adjust one ormore of the IMU parameters (e.g., sample rate). In some embodiments,certain calibration parameters cause the IMU 430 to update an initialposition of the reference point to correspond to a next calibratedposition of the reference point. Updating the initial position of thereference point as the next calibrated position of the reference pointhelps reduce accumulated error associated with determining the estimatedposition. The accumulated error, also referred to as drift error, causesthe estimated position of the reference point to “drift” away from theactual position of the reference point over time.

The electronic display 440 displays 2D or 3D images to the user inaccordance with data received from the console 420. In variousembodiments, the electronic display 440 comprises a single electronicdisplay element (e.g., the electronic display element 355) or multipleelectronic displays (e.g., a display for each eye of a user). Examplesof the electronic display element include: a liquid crystal display(LCD), an organic light emitting diode (OLED) display, an inorganiclight emitting diode (ILED) display, an active-matrix organiclight-emitting diode (AMOLED) display, a transparent organic lightemitting diode (TOLED) display, a waveguide display, some other display,or some combination thereof.

The varifocal block 445 adjusts its focal length by adjusting a focallength of one or more varifocal structures. As noted above withreference to FIG. 3B, the varifocal block 445 adjusts its focal lengthby adjusting a liquid lens structure, e.g., the liquid lens structure100 of FIG. 1 . The varifocal block 445 adjusts its focal lengthresponsive to instructions from the console 420. Note that a varifocaltuning speed of a varifocal structure may be limited by a tuning speedof the liquid lens structure, and accordingly, the liquid lens structureis electrically tuned.

The eye tracking module 450 tracks an eye position and eye movement of auser of the HMD 405. A camera or other optical sensor (that is part theeye tracking module 450) inside the HMD 405 captures image informationof a user’s eyes, and eye tracking module 450 uses the capturedinformation to determine interpupillary distance, interocular distance,a three-dimensional (3D) position of each eye relative to the HMD 405(e.g., for distortion adjustment purposes), including a magnitude oftorsion and rotation (i.e., roll, pitch, and yaw) and gaze directionsfor each eye. In one example, infrared light is emitted within the HMD405 and reflected from each eye. The reflected light is received ordetected by the camera and analyzed to extract eye rotation from changesin the infrared light reflected by each eye. Many methods for trackingthe eyes of a user can be used by eye tracking module 450. Accordingly,the eye tracking module 450 may track up to six degrees of freedom ofeach eye (i.e., 3D position, roll, pitch, and yaw) and at least a subsetof the tracked quantities may be combined from two eyes of a user toestimate a gaze point (i.e., a 3D location or position in the virtualscene where the user is looking). For example, the eye tracking module450 integrates information from past measurements, measurementsidentifying a position of a user’s head, and 3D information describing ascene presented by the electronic display 440. Thus, information for theposition and orientation of the user’s eyes is used to determine thegaze point in a virtual scene presented by the HMD 405 where the user islooking.

The vergence processing module 455 determines a vergence depth of auser’s gaze based on the gaze point or an estimated intersection of thegaze lines determined by the eye tracking module 450. Vergence is thesimultaneous movement or rotation of both eyes in opposite directions tomaintain single binocular vision, which is naturally and automaticallyperformed by the human eye. Thus, a location where a user’s eyes areverged is where the user is looking and is also typically the locationwhere the user’s eyes are focused. For example, the vergence processingmodule 455 triangulates the gaze lines to estimate a distance or depthfrom the user associated with intersection of the gaze lines. The depthassociated with intersection of the gaze lines can then be used as anapproximation for the accommodation distance, which identifies adistance from the user where the user’s eyes are directed. Thus, thevergence distance allows determination of a location where the user’seyes should be focused.

The scene rendering module 460 receives content for the virtual scenefrom an engine 480 and provides the content for display on theelectronic display 440. Additionally, the scene rendering module 460 canadjust the content based on information from the vergence processingmodule 455, the IMU 430, and the position sensors 435. The scenerendering module 460 determines a portion of the content to be displayedon the electronic display 440 based on one or more of a tracking module475, the position sensors 435, or the IMU 430, as described furtherbelow.

The imaging device 410 generates imaging data in accordance withcalibration parameters received from the console 420. Imaging dataincludes one or more images showing observed positions of the locators425 that are detectable by imaging device 410. The imaging device 410may include one or more cameras, one or more video cameras, otherdevices capable of capturing images including one or more locators 425,or some combination thereof. Additionally, the imaging device 410 mayinclude one or more filters (e.g., for increasing signal to noiseratio). The imaging device 410 is configured to detect light emitted orreflected from the locators 425 in a field of view of the imaging device410. In embodiments where the locators 425 include passive elements(e.g., a retroreflector), the imaging device 410 may include a lightsource that illuminates some or all of the locators 425, whichretro-reflect the light towards the light source in the imaging device410. Imaging data is communicated from the imaging device 410 to theconsole 420, and the imaging device 410 receives one or more calibrationparameters from the console 420 to adjust one or more imaging parameters(e.g., focal length, focus, frame rate, ISO, sensor temperature, shutterspeed, aperture, etc.).

The input interface 415 is a device that allows a user to send actionrequests to the console 420. An action request is a request to perform aparticular action. For example, an action request may be to start or endan application or to perform a particular action within the application.The input interface 415 may include one or more input devices. Exampleinput devices include a keyboard, a mouse, a game controller, or anyother suitable device for receiving action requests and communicatingthe received action requests to the console 420. An action requestreceived by the input interface 415 is communicated to the console 420,which performs an action corresponding to the action request. In someembodiments, the input interface 415 may provide haptic feedback to theuser in accordance with instructions received from the console 420. Forexample, haptic feedback is provided by the input interface 415 when anaction request is received, or the console 420 communicates instructionsto the input interface 415 causing the input interface 415 to generatehaptic feedback when the console 420 performs an action.

The console 420 provides content to the HMD 405 for presentation to theuser in accordance with information received from the imaging device410, the HMD 405, or the input interface 415. In the example shown inFIG. 4 , the console 420 includes an application store 470, a trackingmodule 475, and the engine 480. Some embodiments of the console 420 havedifferent or additional modules than those described in conjunction withFIG. 4 . Similarly, the functions further described below may bedistributed among components of the console 420 in a different mannerthan is described here.

The application store 470 stores one or more applications for executionby the console 420. An application is a group of instructions, that whenexecuted by a processor, generates content for presentation to the user.Content generated by an application may be in response to inputsreceived from the user via movement of the HMD 405 or the inputinterface 415. Examples of applications include gaming applications,conferencing applications, video playback application, or other suitableapplications.

The tracking module 475 calibrates the artificial reality system 400using one or more calibration parameters and may adjust one or morecalibration parameters to reduce error in determining position of theHMD 405. For example, the tracking module 475 adjusts the focus of theimaging device 410 to obtain a more accurate position for observedlocators 425 on the HMD 405. Moreover, calibration performed by thetracking module 475 also accounts for information received from the IMU430. Additionally, if tracking of the HMD 405 is lost (e.g., imagingdevice 410 loses line of sight of at least a threshold number oflocators 425), the tracking module 475 re-calibrates some or all of theartificial reality system 400 components.

Additionally, the tracking module 475 tracks the movement of the HMD 405using imaging information from the imaging device 410 and determinespositions of a reference point on the HMD 405 using observed locatorsfrom the imaging information and a model of the HMD 405. The trackingmodule 475 also determines positions of the reference point on the HMD405 using position information from the IMU information from the IMU 430on the HMD 405. Additionally, the tracking module 475 may use portionsof the IMU information, the imaging information, or some combinationthereof, to predict a future location of the HMD 405, which is providedto the engine 480.

The engine 480 executes applications within the artificial realitysystem 400 and receives position information, acceleration information,velocity information, predicted future positions, or some combinationthereof for the HMD 405 from the tracking module 475. Based on thereceived information, the engine 480 determines content to provide tothe HMD 405 for presentation to the user, such as a virtual scene, oneor more virtual objects to overlay onto a real world scene, etc.

In some embodiments, the engine 480 maintains focal capabilityinformation of the varifocal block 445. Focal capability information isinformation that describes what focal distances are available to thevarifocal block 445. Focal capability information may include, e.g., arange of focus the varifocal block 445 is able to accommodate (e.g., 0to 4 diopters settings for the tunable liquid lens structures (e.g.,liquid lens structure 100) that map to particular focal planes.

The engine 480 generates instructions for the varifocal block 445, theinstructions causing the varifocal block 445 to adjust its focaldistance to a particular location. The engine 480 generates theinstructions based on focal capability information and, e.g.,information from the vergence processing module 455, the IMU 430, andthe position sensors 435. The engine 480 uses the information from thevergence processing module 455, the IMU 430, and the position sensors435, or some combination thereof, to select a focal plane to presentcontent to the user. The engine 480 then uses the focal capabilityinformation to determine settings for at least one liquid lens structurewithin the varifocal block 445 that are associated with the selectedfocal plane. The engine 480 generates instructions based on thedetermined settings, and provides the instructions to the varifocalblock 445.

Additionally, the engine 480 performs an action within an applicationexecuting on the console 420 in response to an action request receivedfrom the input interface 415 and provides feedback to the user that theaction was performed. The provided feedback may be visual or audiblefeedback via the HMD 405 or haptic feedback via the input interface 415.

Additional Configuration Information

The foregoing description of the embodiments of the disclosure have beenpresented for the purpose of illustration; it is not intended to beexhaustive or to limit the disclosure to the precise forms disclosed.Persons skilled in the relevant art can appreciate that manymodifications and variations are possible in light of the abovedisclosure.

Some portions of this description describe the embodiments of thedisclosure in terms of algorithms and symbolic representations ofoperations on information. These algorithmic descriptions andrepresentations are commonly used by those skilled in the dataprocessing arts to convey the substance of their work effectively toothers skilled in the art. These operations, while describedfunctionally, computationally, or logically, are understood to beimplemented by computer programs or equivalent electrical circuits,microcode, or the like. Furthermore, it has also proven convenient attimes, to refer to these arrangements of operations as modules, withoutloss of generality. The described operations and their associatedmodules may be embodied in software, firmware, hardware, or anycombinations thereof.

Any of the steps, operations, or processes described herein may beperformed or implemented with one or more hardware or software modules,alone or in combination with other devices. In one embodiment, asoftware module is implemented with a computer program productcomprising a computer-readable medium containing computer program code,which can be executed by a computer processor for performing any or allof the steps, operations, or processes described.

Embodiments of the disclosure may also relate to an apparatus forperforming the operations herein. This apparatus may be speciallyconstructed for the required purposes, and/or it may comprise ageneral-purpose computing device selectively activated or reconfiguredby a computer program stored in the computer. Such a computer programmay be stored in a non-transitory, tangible computer readable storagemedium, or any type of media suitable for storing electronicinstructions, which may be coupled to a computer system bus.Furthermore, any computing systems referred to in the specification mayinclude a single processor or may be architectures employing multipleprocessor designs for increased computing capability.

Embodiments of the disclosure may also relate to a product that isproduced by a computing process described herein. Such a product maycomprise information resulting from a computing process, where theinformation is stored on a non-transitory, tangible computer readablestorage medium and may include any embodiment of a computer programproduct or other data combination described herein.

Finally, the language used in the specification has been principallyselected for readability and instructional purposes, and it may not havebeen selected to delineate or circumscribe the inventive subject matter.It is therefore intended that the scope of the disclosure be limited notby this detailed description, but rather by any claims that issue on anapplication based hereon. Accordingly, the disclosure of the embodimentsis intended to be illustrative, but not limiting, of the scope of thedisclosure, which is set forth in the following claims.

What is claimed is:
 1. A lens comprising: a deformable membranecomprising: a first conductive layer and a second conductive layer, afirst piezoelectric membrane layer positioned between the firstconductive layer and a ground layer, and a second piezoelectric membranelayer positioned between the second conductive layer and the groundlayer, wherein in response to a first voltage being applied to a firstportion of the first conductive layer and a second voltage being appliedto a second portion of the first conductive layer, a first portion ofthe first piezoelectric membrane layer deforms such that a first portionof the deformable membrane has a first curvature associated with a firstoptical power and, concurrently, a second portion of the firstpiezoelectric membrane layer deforms such that a second portion of thedeformable membrane has a second curvature associated with a secondoptical power that is different than the first optical power; and atransparent fluid enclosed between a substrate layer and the deformablemembrane, wherein an optical power of the lens is based in part on anindex of refraction of the transparent fluid.
 2. The lens of claim 1,wherein the substrate layer has a curvature such that the curvatureprovides optical power to the lens.
 3. The lens of claim 1, wherein atleast one of the first conductive layer and the second conductive layercomprises a plurality of non-intersecting conductive wires.
 4. The lensof claim 1, wherein at least one of the first conductive layer and thesecond conductive layer comprises a plurality of conductive wiresarranged in a crosshatch pattern.
 5. The lens of claim 1, wherein,responsive to the first voltage applied to the first conductive layerand the second voltage applied to the first conductive layer, thedeformable membrane curves to provide a fixed optical power to the lens.6. The lens of claim 1, wherein at least one of the first conductivelayer and the second conductive layer comprises a plurality of branchedconductive wires.
 7. The lens of claim 1, wherein at least one of thefirst piezoelectric membrane layer and the second piezoelectric membranelayer is composed of polyvinylidene fluoride.
 8. The lens of claim 1,wherein the lens has a continuous range of optical powers.
 9. The lensof claim 1, wherein the transparent fluid has a refractive index that isbetween 1.2 to 2.5.
 10. The lens of claim 1, wherein the substrate layeris transparent to light in an optical band.
 11. The lens of claim 10,wherein the optical band is selected from a group consisting of visiblelight and infrared light.
 12. A head-mounted display (HMD) comprising: alens comprising: a deformable membrane comprising: a first conductivelayer and a second conductive layer, a first piezoelectric membranelayer positioned between the first conductive layer and a ground layer,and a second piezoelectric membrane layer positioned between the secondconductive layer and the ground layer, wherein in response to a firstvoltage being applied to a first portion of the first conductive layerand a second voltage being applied to a second portion of the firstconductive layer, a first portion of the first piezoelectric membranelayer deforms such that a first portion of the deformable membrane has afirst curvature associated with a first optical power and, concurrently,a second portion of the first piezoelectric membrane layer deforms suchthat a second portion of the deformable membrane has a second curvatureassociated with a second optical power that is different than the firstoptical power; and a transparent fluid enclosed between a substratelayer and the deformable membrane, wherein an optical power of the lensis based in part on an index of refraction of the transparent fluid. 13.The HMD of claim 12, wherein the substrate layer has a curvature suchthat the curvature provides optical power to the lens.
 14. The HMD ofclaim 12, wherein, responsive to the first voltage applied to the firstconductive layer and the second voltage applied to the first conductivelayer, the deformable membrane curves to provide a fixed optical powerto the lens.
 15. The HMD of claim 12, wherein at least one of the firstconductive layer and the second conductive layer comprises a pluralityof branched conductive wires.
 16. The HMD of claim 12, wherein thesubstrate layer is transparent to light in an optical band.